Compression check question

[Davidgsx]

Hey guys! So over the years I've done a few compression tests, recently here on this site I've read that one should leave the spark plugs in the cylinders that aren't being checked, I just can't figure out why that would make any difference.
Just like to know why.


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[96spxpos]

I was told the same thing...I think the logic behind it makes sense..You want to mimic the environment that it would be in under normal operating circumstances. Although the jugs are independent of each other, maybe there are air pockets that would affect the compression reading?

 

[96spxpos]

The whole point of a compression test is to test a component under pressure, and maybe having the other sparkplug in is the closest you can get to a completely sealed, pressurized environment?

 

[SabrToothSqrl]

plugs in would most likely result in a lower rating as the cranking speed would be lower.

Also, I prefer the ride it test.

 

[Sportster-2001-951C-Stock]

Yep, remove all spark plugs in case one of the piston springs are broken.

 

[Sportster-2001-951C-Stock]

Seriously guys, remove all spark plugs.

 

[doomann88]

Oh no not the piston springs!

 

[Davidgsx]

Dude I had a piston spring pop right out the spark plug hole once!!!


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[Sportster-2001-951C-Stock]

Yes, good example! When that happens it's usually b/c one spark plug was removed while the other was still in. This can pop the piston return springs right out of there within a couple revolutions of the rotating assembly, even when rotated by hand.

However, if it begins to run with one spark plug removed the imbalance could seize a muffler bearing.

 

[Davidgsx]

Wow, your good at that, I almost started believing it!!


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[SabrToothSqrl]

Did you check the halogen headlight fluid?

 

[Coastiejoe]

And we will come back to finding the key to the sea chest once again...

And while you are at it, get me 100 feet of shore line would ya?

 

[LouDoo]

I need a bucket of prop wash, also does anyone have a spare knuter valve? Seriously removing both spark plugs makes it easier on the starting system.

Lou

 

[jammin777]

However, if it begins to run with one spark plug removed the imbalance could seize a muffler bearing.

it wouldn't seize if you changed the muffler fluid.

 

[jhjesse]

So David I was just reading your other thread...outta control. Now this thread is starting to go the same direction. LOL

Folks it's only November! Are we already starting to have symptoms of Cabin Fever??? :willy_nilly:

 

[Coastiejoe]

Cold weather panic always sets in early.


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[soccerdad]

Rain and snow flurries here in Greensboro NC today 4-6" of snow in the mountains. IT WAS 80 earlier this week.

 

[AdamXP800]

Yea, I got snow in Augusta GA this morning. Was 80 a few days ago

 

[Davidgsx]

So David I was just reading your other thread...outta control. Now this thread is starting to go the same direction. LOL

Folks it's only November! Are we already starting to have symptoms of Cabin Fever??? :willy_nilly:

What is it about my threads that makes that happen?!!

I think it's awesome!! My wife thinks I'm crazy cause I keep laughing at my phone!!



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[96spxpos]

Ok all jokes aside.. Some of you guys are so good at this stuff, it's hard to tell who's serious..
Anyway, so
Best way for a compression test:
Keeping the spark plug IN the other cylinder, but having the BOOT off (you guys were concerned about the ski starting/firing and messing up the exhaust, yet it wouldn't start without the wire/boot on it, right?)

Or just leaving the other cylinder COMPLETELY OPEN?

 

[Davidgsx]

I'm going with plugs out, F it!!


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[AdamXP800]

Just leave the plugs out and wires grounded.

 

[96spxpos]

Lol, ok, well as long as that isn't "cheating"! Like a dude tells you it's got 140psi in each jug by doing it that way, and it really only has 120psi by keeping 1 plug in. But sounds good to me! Plugs out, Jugs out!!

 

[Sportster-2001-951C-Stock]

All plugs out, throttle wide open, fuel off (if possible), wires grounded is the right way, otherwise the readings will be totally wrong (and unpredictable). Whomever told you guys to leave plugs in, they were pulling your leg, plain wrong.

Aside: Turning off the fuel (when/if possible) can help avoid unanticipated "dumpster explosion hairdo" and similar "brown events" from occurring!

 

[96spxpos]

Hahahaha brown events... I can only speculate you're referring to "Personal Shartation Device"....